The present invention relates to a cordless telephone and, more particularly, to a cordless telephone having a fixed unit and a portable unit which exchange an identification signal assigned to the own telephone.
As well known in the art, a cordless telephone is made up of a fixed unit, or part which is connected to a subscriber line, and a portable unit, or part, which is connected to the fixed unit by a radio link. Generally a particular identification (ID) number is assigned to each cordless telephone so as to avoid interference and erroneous connection between the independent cordless telephones. There is known a system which causes the ID number to be exchanged as an ID signal between a fixed and a portable units of a cordless telephone even when a conversation is under way, thereby allowing the two units to identify each other continuously till the end of conversation. In this prior art system, while one of the two cooperative units transmits the ID signal, the other responds to and identifies the ID signal and, then, returns it, i.e., the fixed and portable units enable a communication to be held while confirming the ID signal.
The prior art cordless telephone as discussed above has a relatively simple radio circuit construction so that the ID signal of the kind stated is usually implemented with an audible frequency. The problem is, therefore, that the ID signal returned from the fixed unit to the portable unit is heard through a speaker to be offensive to the ear very much.